Chapter 11
SOUTH CAROLINA
GEOLOGY AND SEISMICITY
Final
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Table of Contents
Page
Introduction....................................................................................................... 11-1
South Carolina Geology ................................................................................... 11-2
Blue Ridge Unit ................................................................................................ 11-5
Piedmont Unit................................................................................................... 11-5
“Fall Line” ....................................................................................................... 11-6
Coastal Plain Unit............................................................................................. 11-6
11.6.1 Lower Coastal Plain.............................................................................. 11-8
11.6.2 Middle Coastal Plain............................................................................. 11-8
11.6.3 Upper Coastal Plain.............................................................................. 11-8
11.7 South Carolina Seismicity ................................................................................ 11-9
11.7.1 Central and Eastern United States (CEUS) Seismicity ........................ 11-9
11.7.2 SC Earthquake Intensity..................................................................... 11-10
11.8 South Carolina Seismic Sources.................................................................... 11-11
11.8.1 Non-Characteristic Earthquake Sources ............................................ 11-11
11.8.2 Characteristic Earthquake Sources .................................................... 11-13
11.9 South Carolina Earthquake Hazard................................................................ 11-14
11.9.1 Design Earthquakes ........................................................................... 11-14
11.9.2 Probabilistic Earthquake Hazard Maps .............................................. 11-15
11.9.3 Earthquake Deaggregation Charts ..................................................... 11-27
11.9.4 Ground Motions .................................................................................. 11-30
11.10 References ..................................................................................................... 11-35
Section
11.1
11.2
11.3
11.4
11.5
11.6
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List of Tables
Page
Table
Table 11-1, Modified Mercalli Intensity Scale (MMIS)................................................ 11-10
Table 11-2, Source Areas for Non-Characteristic Background Events ...................... 11-12
Table 11-3, SCDOT Design Earthquakes .................................................................. 11-15
Table 11-4, Coastal Plain Geologically Realistic Model............................................. 11-16
Table 11-5, Geologically Realistic Model Outside of Coastal Plain ........................... 11-17
Table 11-6, Site Conditions........................................................................................ 11-17
Table 11-7, Latitude and Longitude for South Carolina Cities ................................... 11-18
Table 11-8, USGS Interactive Deaggregation of Seismic Hazard ............................. 11-27
Table 11-9, Location of Ground Motion...................................................................... 11-31
Table 11-10, FEE 1Hz PSA Deaggregation Summary - Anderson, SC..................... 11-32
Table 11-11, SEE 1Hz PSA Deaggregation Summary - Anderson, SC..................... 11-32
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List of Figures
Page
Figure
Figure 11-1, South Carolina Physiographic Units ........................................................ 11-2
Figure 11-2, 2005 Generalized Geologic Map of South Carolina, (SCDNR) ............... 11-3
Figure 11-3, Geologic Time Scale for South Carolina (SCDNR) ................................. 11-4
Figure 11-4, South Carolina “Fall Line” ........................................................................ 11-6
Figure 11-5, Contour Map of Coastal Plain Sediment Thickness, in meters................ 11-7
Figure 11-6, U.S. Earthquakes Causing Damage 1750 – 1996 (USGS) ..................... 11-9
Figure 11-7, SC Earthquake Intensities By County (SCDNR) ................................... 11-10
Figure 11-8, Source Areas for Non-Characteristic Earthquakes................................ 11-11
Figure 11-9, Alternative Source Areas for Non-Characteristic Earthquakes.............. 11-12
Figure 11-10, Southeastern U.S. Earthquakes (MW > 3.0 from 1600 to Present) ...... 11-13
Figure 11-11, South Carolina Characteristic Earthquake Sources ............................ 11-14
Figure 11-12, SCDOT Site Condition Selection Map ................................................. 11-16
Figure 11-13, Scenario_PC (2006) Sample Output for Columbia, SC....................... 11-18
Figure 11-14, PGA (%g) - 15% PE in 75 Years (10% PE-50 Yr)................................. 11-20
Figure 11-15, Ss Spectral Acceleration (%g) - 15% PE in 75 Years (10% PE-50 Yr).. 11-21
Figure 11-16, S1 Spectral Acceleration (%g) - 15% PE in 75 Years (10% PE-50 Yr).. 11-22
Figure 11-17, PGA (%g) - 3% PE in 75 Years (2% PE-50 Yr)..................................... 11-23
Figure 11-18, Ss Spectral Acceleration (%g) - 3% PE in 75 Years (2% PE-50 Yr)...... 11-24
Figure 11-19, S1 Spectral Acceleration (%g) - 3% PE in 75 Years (2% PE-50 Yr)...... 11-25
Figure 11-20, FEE PSA Curves for Selected South Carolina Cities .......................... 11-26
Figure 11-21, SEE PSA Curves for Selected South Carolina Cities .......................... 11-26
Figure 11-22, Scenario_PC (2006) Deaggregation – Columbia, SC ......................... 11-27
Figure 11-23, Interactive Deaggregation Input Screen .............................................. 11-28
Figure 11-24, Columbia, SC Deaggregation SEE (3% PE in 75 Years, 1Hz PSA)..... 11-28
Figure 11-25, Abridged Seismic Hazard Matrix Data – Columbia, SC....................... 11-29
Figure 11-26, Geographic Deaggregation (Optional)................................................. 11-29
Figure 11-27, Florence, SC Deaggregation FEE (15% PE in 75 Years, 1Hz PSA) .... 11-33
Figure 11-28, Florence, SC Deaggregation SEE (3% PE in 75 Years, 1Hz PSA)...... 11-33
Figure 11-29, Anderson, SC Deaggregation FEE (15% PE in 75 Years, 1Hz PSA) .. 11-34
Figure 11-30, Anderson, SC Deaggregation SEE (3% PE in 75 Years, 1Hz PSA)..... 11-34
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CHAPTER 11
SOUTH CAROLINA GEOLOGY AND SEISMICITY
11.1
INTRODUCTION
This Chapter describes South Carolina’s basic geology and seismicity within the context of
performing geotechnical engineering for the SCDOT. It is anticipated that the material
contained in this Chapter will establish a technical framework by which basic geology and
seismicity can be addressed. It is not intended to be an in-depth discussion of all the geologic
formations and features found in South Carolina (SC) or a highly technical discussion of the
state’s seismicity. The designers are expected to have sufficient expertise in these technical
areas and to have the foresight and resourcefulness to keep up with the latest advancements in
these areas.
The State of South Carolina is located in the Southeastern United States and is bounded on the
north by the State of North Carolina, on the west and the south by the State of Georgia, and on
the east by the Atlantic Ocean. The State is located between Latitudes 32° 4' 30" N and
35° 12' 00” N and between Longitudes 78° 0' 30" W and 83° 20' 00” W. The State is roughly
triangular in shape and measures approximately 260 miles East-West and approximately 200
miles North-South at the states widest points. The South Carolina coastline is approximately
187 miles long. South Carolina is ranked 40th in size with an approximate area of 30,111 square
miles.
The geology of South Carolina is similar to that of the neighboring states of Georgia, North
Carolina, and Virginia. These states have in the interior the Appalachian Mountains with an
average elevation of 3,000 feet followed by the Appalachian Piedmont that typically ranges in
elevation from 300 feet to 1000 feet. Continuing eastward from these highlands is a “Fall Line”
which serves to transition into the Atlantic Coastal Plain. The Atlantic Coastal Plain gently
slopes towards the Atlantic Ocean with few elevations higher than 300 feet.
The 1886 earthquake that occurred in the Coastal Plain near Charleston, South Carolina
dominates the seismic history of the southeastern United States. It is the largest historic
earthquake in the southeastern United States with an estimated moment magnitude, MW, of 7.3.
The damage area with a Modified Mercalli Intensity Scale of X, is an elliptical shape roughly 20
by 30 miles trending northeast between Charleston and Jedburg and including Summerville and
roughly centered at Middleton Place. The intraplate epicenter of this earthquake and it’s
magnitude is not unique in the Central and Eastern United States (CEUS). Other intraplate
earthquakes include those at Cape Ann, Massachusetts (1755) with a MW of 5.9, and the New
Madrid, Missouri (1811-1812) with MW of at least 7.7.
The following sections describe the basic geology of South Carolina and the seismicity that will
be used to perform geotechnical engineering designs and analyses. The topics discussed in
these sections will be referenced throughout this Manual.
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SOUTH CAROLINA GEOLOGY
South Carolina geology can be divided into three basic physiographic units: Blue Ridge Unit
(Appalachian Mountains), Piedmont Unit, and the Coastal Plain Unit. The generalized locations
of these physiographic units are shown in Figure 11-1.
Figure 11-1, South Carolina Physiographic Units
(Snipes et al., 1993)
The Blue Ridge Unit (Appalachian Mountains) covers approximately 2 percent of the state and it
is located in the northwestern corner of the state. The Piedmont Unit comprises approximately
one-third of the state with the Coastal Plain Unit covering the remaining two-thirds of the state.
The geologic formations are typically aligned from the South-Southwest to the North-Northeast
and parallel the South Carolina Atlantic coastline as shown in the generalized geologic map in
Figure 11-2. The physiographic units in Figure 11-2 are broken down by the geologic time of
the surface formations. South Carolina formations span in age from late Precambrian through
the Quaternary period. The descriptions of events that have occurred over geologic time in
South Carolina are shown in Figure 11-3.
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Figure 11-2, 2005 Generalized Geologic Map of South Carolina, (SCDNR)
A description of the geologic formations, age, and geologic features for the Blue Ridge,
Piedmont, and Coastal Plain Physiographic Units are provided in the following sections.
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Figure 11-3, Geologic Time Scale for South Carolina (SCDNR)
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SC GEOLOGY AND SEISMICITY
BLUE RIDGE UNIT
The Blue Ridge Unit consists of mountains that are part of the Blue Ridge Mountains and is a
southern continuation of the Appalachian Mountains. The Brevard Fault zone (depicted as the
Brevard zone, BZ, in Figure 11-2) separates the Blue Ridge Unit from the Piedmont Unit. It
consists of metamorphic and igneous rocks. The topography is rugged and mountainous and
contains the highest elevations in the State of South Carolina with elevations ranging from 1,400
feet to 3,500 feet. Sassafras Mountain is the highest point in South Carolina with an elevation
of 3,560 feet. The Appalachian Mountains were formed in the late Paleozoic era, about 342
million years ago (MYA). The basement rocks in the Blue Ridge Unit were formed in the late
Precambrian time period (570 to 2,500 MYA). The oldest rock dated in South Carolina is 1,200
million years old.
The bedrock in this region is a complex crystalline formation that has been faulted and contorted
by past tectonic movements. The rock has weathered to residual soils that form the mantle for
the hillsides and hilltops. The typical residual soil profile in areas not disturbed by erosion or the
activities of man consists of clayey soils near the surface where weathering is more advanced,
underlain by sandy silts and silty sands. There may be colluvial (old land-slide) material on the
slopes.
11.4
PIEDMONT UNIT
The Piedmont Unit is bounded on the west by the Blue Ridge Unit and on the east by the
Coastal Plain Unit. The boundary between the Blue Ridge Unit and the Piedmont Unit is
typically assumed to be the Brevard Fault zone (depicted as the Brevard zone, BZ, in Figure 112). The common boundary between the Piedmont Unit and the Coastal Plain Unit is the “Fall
Line”. It is believed that the Piedmont is the remains of an ancient mountain chain that has
been eroded with existing elevations ranging from 300 feet to 1,400 feet. The Piedmont is
characterized by gently rolling topography, deeply weathered bedrock, and relatively few rock
outcrops. It contains monadnocks that are isolated outcrops of bedrock (usually quartzite or
granite) that are a result of the erosion of the mountains. The vertical stratigraphic sequence
consists of 5 to 70 feet of weathered residual soils at the surface underlain by metamorphic and
igneous basement rocks (granite, schist, and gneiss). The weathered soils (saprolites) are
physically and chemically weathered rocks that can be soft/loose to very hard and dense, or
friable and typically retain the structure of the parent rock. The geology of the Piedmont is
complex with numerous rock types that were formed during the Paleozoic era (250 to 570
MYA).
The typical residual soil profile consists of clayey soils near the surface, where soil weathering is
more advanced, underlain by sandy silts and silty sands. The boundary between soil and rock
is not sharply defined. This transitional zone termed “partially weathered rock” (PWR) is
normally found overlying the parent bedrock. Partially weathered rock is defined, for
engineering purposes, as residual material with Standard Penetration Test resistances in
excess of 100 blows/foot. The partially weathered rock is considered in geotechnical
engineering as an Intermediate Geomaterial (IGM). Weathering is facilitated by fractures, joints,
and by the presence of less resistant rock types. Consequently, the profile of the partially
weathered rock and hard rock is quite irregular and erratic, even over short horizontal distances.
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Also, it is not unusual to find lenses and boulders of hard rock and zones of partially weathered
rock within the soil mantle, well above the general bedrock level.
11.5
“FALL LINE”
A “Fall Line” is an unconformity that marks the boundary between an upland region (bed rock)
and a coastal plain region (sediment). In South Carolina the Piedmont Unit is separated from
the Coastal Plain Unit by a “Fall Line” that begins near the Edgefield-Aiken County line and
traverses to the northeast through Lancaster County. In addition to Columbia, SC many cities
were built along the “Fall Line” as it runs up the east coast (Macon, Raleigh, Richmond,
Washington D.C., and Philadelphia). The “Fall Line” generally follows the southeastern border
of the Savannah River terrane formation and the Carolina terrane (slate belt) formation shown in
Figure 11-2. Along the “Fall Line” between elevations 300 to 725, the Sandhills formations can
be found which are the remnants of a prehistoric coastline. The Sandhills are unconnected
bands of sand deposits that are remnants of coastal dunes that were formed during the Miocene
epoch (5.3 to 23 MYA). The land to the southeast of the “Fall Line” is characterized by a gently
downward sloping elevation (2 to 3 feet per mile) as it approaches the Atlantic coastline as
shown in Figure 11-4. Several rivers such as the Pee Dee, Wateree, Lynches, Congaree, N.
Fork Edisto, and S. Fork Edisto flow from the “Fall Line” towards the Atlantic coast as they cut
through the Coastal Plain sediments.
Figure 11-4, South Carolina “Fall Line”
(Odum et al., 2003)
11.6
COASTAL PLAIN UNIT
The Coastal Plain Unit is a compilation of wedge shaped formations that begin at the “Fall Line”
and dip towards the Atlantic Ocean with ground surface elevations typically less than 300 feet.
The Coastal Plain is underlain by Mesozoic/Paleozoic basement rock. This wedge of sediment
is comprised of numerous geologic formations that range in age from late Cretaceous period to
Recent. The sedimentary soils of these formations consist of unconsolidated sand, clay, gravel,
marl, cemented sands, and limestone that were deposited over the basement rock. The marl
and limestone are considered in geotechnical engineering as an IGM. The basement rock
consists of granite, schist, and gneiss similar to the rocks of the Piedmont Unit. The thickness
of the Coastal Plain sediments varies from zero at the “Fall Line” to more than 4,000 feet at the
southern tip of South Carolina near Hilton Head Island. The thickness of the Coastal Plain
sediments along the Atlantic coast varies from ~1300 feet at Myrtle Beach to ~4000 feet at
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Hilton Head Island. The top of the basement beneath the Coastal Plain has been mapped
during a SC Seismic Hazard Study that was prepared for SCDOT and the contours of the
Coastal Plain sediment thickness in meters are shown in Figure 11-5.
The area is formed of older, generally well-consolidated layers of sands, silts, or clays that were
deposited by marine or fluvial action during a period of retreating ocean shoreline.
Predominantly, sediments lie in nearly horizontal layers; however, erosional episodes occurring
between depositions of successive layers are often expressed by undulations in the contacts
between the formations. Due to their age, sediments exposed at the ground surface are often
heavily eroded. Ridges and hills are either capped by terrace gravels or wind-deposited sands.
Younger alluvial soils may mask these sediments in swales or stream valleys.
Figure 11-5, Contour Map of Coastal Plain Sediment Thickness, in meters
(Chapman and Talwani, 2002)
This Coastal Plain Unit was formed during Quaternary, Tertiary, and late Cretaceous geologic
periods. The Coastal Plain can be divided into the following three subunits:



Upper Coastal Plain
Middle Coastal Plain
Lower Coastal Plain
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The Lower Coastal Plain comprises approximately one-half of the entire Atlantic Coastal Plain of
South Carolina. The Surry Scarp (-SS-) shown in Figure 11-2 separates the Lower Coastal
Plain from the Middle Coastal Plain. The Surry Scarp is a seaward facing scarp with a toe
elevation of 90 to 100 feet. The Middle Coastal Plain and the Upper Coastal Plain each
compose approximately one fourth of the Coastal Plain area. The Orangeburg Scarp (-OS-)
shown in Figure 11-2 separates the Middle Coastal Plain from the Upper Coastal Plain. The
Orangeburg Scarp is also a seaward facing scarp with a toe elevation of 250 to 270 feet.
11.6.1
Lower Coastal Plain
The Lower Coastal Plain is typically identified as the area east of the Surry Scarp below
elevation 100 feet. The vertical stratigraphic sequence overlying the basement rock consists of
unconsolidated Cretaceous, Tertiary, and Quaternary sedimentary deposits. The surface
deposits of the Lower Coastal Plain were formed during the Quaternary period that began
approximately 1.6 MYA and extends to present day. The Quaternary period can be further
subdivided into the Pleistocene epoch and the Holocene epoch. During the Pleistocene epoch
(1.6 MYA to 10 thousand years ago) the surficial deposits that cover the underlying Coastal
Plain formations were formed. This period specifically marks the formation of the Carolina Bays
and scarps throughout the east coast due to sea level rise and fall. The Holocene epoch covers
from 10 thousand years ago to present day. Barrier islands were formed and flood plains from
major rivers were formed during the Holocene epoch. Preceding Quaternary period during the
Eocene epoch (53 to 36.6 MYA) of the Tertiary period, limestone was deposited in the Lower
Coastal Plain.
11.6.2
Middle Coastal Plain
The Middle Coastal Plain is typically identified as the area between the Orangeburg Scarp and
the Surry Scarp and falls between elevation 100 feet and 270 feet. The vertical stratigraphic
sequence overlying the basement rock consists of unconsolidated Cretaceous and Tertiary
sedimentary deposits. The surface deposits of the Middle Coastal Plain were formed during the
Pliocene epoch of the Tertiary period. During the Pliocene epoch (5.3 to 1.6 MYA) of the
Tertiary period, the Orangeburg Scrap was formed as a result of scouring from the regressive
cycles of the Ocean as it retreated. During the Eocene epoch (53 to 36.6 MYA) of the Tertiary
period, limestone was deposited in the Middle Coastal Plain.
11.6.3
Upper Coastal Plain
The Upper Coastal Plain is typically identified as the area between the “Fall Line” and the
Orangeburg Scarp and falls between elevations 270 feet and 300 feet. The Upper Coastal Plain
was formed during the Tertiary and late Cretaceous periods. The Tertiary period began
approximately 65 MYA and ended approximately 1.6 MYA. The Tertiary period can be further
subdivided into the Pliocene epoch, Miocene epoch, Oligocene epoch, Eocene epoch, and
Paleocene epoch. The Miocene epoch (23 to 5.3 MYA) is marked by the formation of the
Sandhills dunes as a result of fluvial deposits over the Coastal Plain. During the early Tertiary
period (65 to 23 MYA) fluvial deposits over the Coastal Plain consisted of marine sediments,
limestone, and sand.
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11.7.1
SC GEOLOGY AND SEISMICITY
SOUTH CAROLINA SEISMICITY
Central and Eastern United States (CEUS) Seismicity
Even though seismically active areas in the United States are generally considered to be in
California and Western United States, historical records indicate that there have been major
earthquake events in Central and Eastern United States (CEUS) that have not only been of
equal or greater magnitude but that have occurred over broader areas of the CEUS. The United
States Geologic Survey (USGS) map shown in Figure 11-6 indicates earthquakes that have
caused damage within the United States between 1750 and 1996. Of particular interest to
South Carolina is the 1886 earthquake in Charleston, SC that has been estimated to have a MW
of at least 7.3. Also of interest to the northwestern end of South Carolina is the influence of
New Madrid seismic zone, near New Madrid, Missouri, where historical records indicate that
between 1811 and 1812 there were several large earthquakes with a MW of at least 7.7.
Figure 11-6, U.S. Earthquakes Causing Damage 1750 – 1996 (USGS)
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SC GEOLOGY AND SEISMICITY
SC Earthquake Intensity
The Modified Mercalli Intensity Scale (MMIS) is a qualitative measure of the strength of ground
shaking at a particular site that is used in the United States. Each earthquake large enough to
be felt will have a range of intensities. Typically the highest intensities are measured near the
earthquake epicenter and lower intensities are measured farther away. The MMIS is used to
distinguish the ground shaking at geographic locations as opposed to the moment magnitude
scale that is used to compare the energy released by earthquakes. Roman numerals are used
to identify the MMIS of ground shaking with respect to shaking and damage felt at a geographic
location as shown in Table 11-1.
Table 11-1, Modified Mercalli Intensity Scale (MMIS)
INTENSITY
I
II –
III
IV
V
VI
VII
VIII
IX
X+
SHAKING
Not
Felt
Weak
Light
Moderate
Strong
Very
Strong
Severe
Violent
Extreme
DAMAGE
None
None
None
Very
Light
Light
Moderate
Moderate
/ Heavy
Heavy
Very
Heavy
Figure 11-7 shows a map developed by the South Carolina Geological Survey with earthquake
intensities, by county, based on the MMIS. The intensities shown on this map are the highest
likely under the most adverse geologic conditions that would be produced by a combination of
the August 31, 1886, Charleston, S.C. earthquake (MW = 7.3) and the January 1, 1913, Union
County, S.C., earthquake (MW = 5.5). This map is for informational purposes only and is not
intended as a design tool, but reflects the potential for damage based on earthquakes similar to
the Union and Charleston earthquake events.
Figure 11-7, SC Earthquake Intensities By County (SCDNR)
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SOUTH CAROLINA SEISMIC SOURCES
Sources of seismicity are not well defined in much of the Eastern United States. South Carolina
seismic sources have therefore been defined based on seismic history in the Southeastern
United States. The SC Seismic Hazard study (Chapman and Talwani, 2002) has identified two
types of seismic sources: Non-Characteristic Earthquakes and Characteristic Earthquakes.
11.8.1
Non-Characteristic Earthquake Sources
Seismic histories were used to establish seismic area sources for analysis of non-characteristic
background events. The study modified the Frankel et al., 1996 source area study to develop
the seismic source areas shown in Figures 11-8 and 11-9.
Figure 11-8, Source Areas for Non-Characteristic Earthquakes
(Chapman and Talwani, 2002)
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Figure 11-9, Alternative Source Areas for Non-Characteristic Earthquakes
(Chapman and Talwani, 2002)
The source areas listed in Figures 11-8 and 11-9 are described in Table 11-2.
Table 11-2, Source Areas for Non-Characteristic Background Events
(Chapman and Talwani, 2002)
Area
Description
Area
Area
Description
Area
(sq.miles)
No.
(sq.miles) No.
Zone 1
8,133
Alabama
20,257
1
10
Zone 2
2,475
Eastern Tennessee
14,419
2
11
Central Virginia
7,713
Southern Appalachian
29,234
3
12
Zone 4
9,687 12a Southern Appalachian N.
17,034
4
Zone 5
18,350
Giles County, VA
1,980
5
13
Piedmont and Coastal Plain
161,110
Central Appalachians
16,678
6
14
Piedmont & CP NE
18,815
West Tennessee
29,667
6a
15
Piedmont & CP SW
95,854
Central Tennessee
20,630
6b
16
SC Piedmont
22,248
Ohio – Kentucky
58,485
7
17
Middleton Place
455
West VA-Pennsylvania
34,049
8
18
Florida/Continental Margin
110,370
USGS Gridded Seis.--9
19
1996
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Figure 11-10 shows additional historical seismic information obtained from the Virginia Tech
catalog of seismicity in the Southeastern United States from 1600 to present that was used to
model the non-characteristic background events in the source areas.
Figure 11-10, Southeastern U.S. Earthquakes (MW > 3.0 from 1600 to Present)
(Chapman and Talwani, 2002)
11.8.2
Characteristic Earthquake Sources
The single most severe earthquake that has occurred in South Carolina’s human history
occurred in Charleston, South Carolina, in 1886. It was one of the largest, earthquakes to affect
the Eastern United States in historical times. The MW of this earthquake has been estimated to
range from 7.0 to 7.5. It is typically referred to have a MW of 7.3. The faulting source that was
responsible for the 1886 Charleston earthquake remains uncertain to date.
Large magnitude earthquake events with the potential to occur in coastal South Carolina are
considered characteristic earthquakes. These earthquakes are modeled as a combination of
fault sources and a seismic Area Source. The SC Seismic Hazard study used the 1886
Earthquake fault source, also known as the Middleton Place seismic zone, and the “Zone of
River Anomalies” (ZRA) fault source. For the 1886 Earthquake fault source it assumed that
rupture occurred on the NE trending “Woodstock” fault and on the NW trending “Ashley River”
fault. The 1886 Earthquake fault source is modeled as three independent parallel faults.
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Recent studies (Marple and Talwani, 1993, 2000) suggest that the “Woodstock” fault may be a
part of larger NE trending fault system that extends to North Carolina and possibly Virginia,
referred to in the literature as the “East Coast Fault System”. The ZRA fault source is the term
used for the portion of the “East Coast Fault System” that is located within South Carolina. The
ZRA fault system is modeled by a 145-mile long fault with a NE trend. The characteristic
seismic Area Source is the same as is used in the 1996 National Seismic Hazard Maps. It
models a network of individual faults no greater than 46 miles in length within the Lower Coastal
Plain. The fault sources and area sources used to model the characteristic earthquake sources
in the SC Seismic Hazard Study are shown in Figure 11-11.
Figure 11-11, South Carolina Characteristic Earthquake Sources
(Chapman and Talwani, 2002)
11.9
11.9.1
SOUTH CAROLINA EARTHQUAKE HAZARD
Design Earthquakes
The SCDOT uses a Functional Evaluation Earthquake (FEE) and a Safety Evaluation
Earthquake (SEE) to design transportation infrastructure in South Carolina. The FEE
represents a small ground motion that has a likely probability of occurrence within the life of the
structure being designed. The SEE represents a large ground motion that has a relatively low
probability of occurrence within the life of the structure. The two levels of earthquakes have
been chosen for South Carolina because SEE spectral accelerations can be as much as three
to four times higher than FEE spectral accelerations in the Eastern United States. In contrast,
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the California SEE spectral accelerations can be the same or as much as 1.8 times the FEE
spectral accelerations. Because of the large variation between FEE and SEE design
earthquake events it is necessary to perform geotechnical earthquake engineering analyses for
each event and compare the resulting performance with the SCDOT Performance Limits
established in Chapter 10. The design life for transportation infrastructure is typically assumed
to be 75 years when evaluating the design earthquakes, regardless of the actual design life
specified in Chapter 10. The likelihood of these events occurring is quantified by the design
events probability of exceedance (PE) within the design life of the structure. Descriptions of the
design earthquakes used in South Carolina are provided in Table 11-3.
Table 11-3, SCDOT Design Earthquakes
Design Earthquake
Description
The ground shaking having a 15 percent
probability of exceedance in 75 years (15%/75
year). This design earthquake is equal to the 10
Functional Evaluation Earthquake (FEE) percent probability of exceedance in 50 years
(10%/50). The FEE PGA and PSA are used for
the functional evaluation of transportation
infrastructure.
The ground shaking having a 3 percent probability
of exceedance in 75 years (3%/75 year). This
design earthquake is equal to the 2 percent
Safety Evaluation Earthquake (SEE)
probability of exceedance in 50 years (2%/50).
The SEE PGA and PSA are used for the safety
evaluation of transportation infrastructure.
11.9.2
Probabilistic Earthquake Hazard Maps
A SC Earthquake Hazard study was completed for SCDOT In October 2006 (Chapman and
Talwani, 2002 and Chapman, 2006). The study produced probabilistic seismic hazard maps
that reflect the actual geological conditions in South Carolina. The seismic hazard maps are
motion intensities for a specific probability of exceedance (PE). The motions are defined in
terms of pseudo-spectral accelerations (PSA) at frequencies of 0.5, 1.0, 2.0, 3.3, 5.0, 6.67, and
13.0 Hz, for a damping ratio of 0.05 (5%) and the peak horizontal ground acceleration (PHGA or
PGA). These accelerations were developed for the geologically realistic site conditions as well
as for the hypothetical hard-rock basement outcrop. The geologically realistic site condition is a
hypothetical site condition that was developed by using a transfer function of a linear response.
South Carolina has been divided into two zones as shown in Figure 11-12: Zone I –
Physiographic Units Outside of the Coastal Plain and Zone II – Coastal Plain Physiographic
Unit. The delineation between these two zones has been shown linearly in Figure 11-12 but in
reality it should follow the “Fall Line.” Because of the distinct differences between these two
physiographic units, a geologically realistic model has been developed for each zone.
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Figure 11-12, SCDOT Site Condition Selection Map
(Modified Chapman and Talwani, 2002)
The Coastal Plain geologically realistic site condition consists of two layers, the shallowest layer
consists of Coastal Plain sedimentary soil (Q=100) and weathered rock (Q=600), over a
half-space of unweathered Mesozoic and Paleozoic sedimentary, and Metamorphic/Igneous
rock, assuming vertical shear wave incidence.
The soil properties for the Coastal Plain
geologically realistic model are shown in Table 11-4.
The Piedmont geologically realistic site condition consists of one layer of weathered rock
(Q=600) over a half-space of unweathered Mesozoic and Paleozoic sedimentary, and
Metamorphic/Igneous rock, assuming vertical shear wave incidence. The soil properties for the
Piedmont geologically realistic model are shown in Table 11-5.
Table 11-4, Coastal Plain Geologically Realistic Model
Total Unit
Shear Wave
Mass Density, 
Soil Layer
Velocity, VS
Weight, 
3
kg/m
pcf
ft/sec
Layer 1 – Sedimentary Soils
2,000
125
2,300
Layer 2 – Weathered Rock
2,500
155
8,200
Half-Space – Basement Rock
2,600
165
11,200
11-16
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Table 11-5, Geologically Realistic Model Outside of Coastal Plain
Total Unit
Shear Wave
Mass Density, 
Soil Layer
Velocity, VS
Weight, 
3
pcf
ft/sec
kg/m
Layer 1 – Weathered Rock
2,500
155
8,200
Half-Space - Basement Rock
2,600
165
11,200
The transfer functions were computed using ¼ wavelength approximation of Boor and Joyner
(1991). For more information on the development of the transfer function refer to Chapman and
Talwani (2002).
The selection of the appropriate site condition is very important in the generation of probabilistic
seismic hazard motions in the form of pseudo-spectral accelerations (PSA) and the peak
horizontal ground acceleration (PHGA or PGA). The available site conditions for use in
generating probabilistic seismic hazard motions are defined in Table 11-6. The selection of the
appropriate site condition should be based on the results of the geotechnical site investigation,
geologic maps, and any available geologic or geotechnical information from past projects in the
area. Generally speaking the geologically realistic site condition should be used in the Coastal
Plain. In areas outside of the Coastal Plain such as the Piedmont / Blue Ridge Physiographic
Units and along the “Fall Line” should be evaluated carefully. The geotechnical investigation in
these areas should be sufficiently detailed to determine depth to weathered rock having a shear
wave velocity of approximately 8,000 to 8,200 ft/sec or to define the basement rock outcrop
having a shear wave greater than 11,000 ft/sec.
Table 11-6, Site Conditions
Site Condition
South Carolina
Zones
Zone I –
Physiographic Units
Outside of the
Coastal Plain
Zone II – Coastal
Plain Physiographic
Unit
Geologically
Realistic
Hypothetical outcrop of “Weathered
Southeastern U.S. Piedmont Rock” that
consist of 820 feet thick weathered formation
of shear wave velocity, Vs = 8,000 ft/s
overlying a hard-rock formation having shear
wave velocity, Vs = 11,500 ft/s.
Hypothetical outcrop of “Firm Coastal Plain
Sediment” equivalent to the B-C Boundary
having a shear wave velocity, Vs = 2,500 ft/s.
Hard-Rock
Basement
Outcrop
A hard-rock
basement outcrop
formation having
shear wave
velocity,
Vs = 11,500 ft/s.
The seismic hazards computations use the seismic sources listed in Section 11.8, the design
earthquake in Section 11.9.1, and the ground motions described in Section 11.9.4.
The PGA and PSA can be obtained for any location in South Carolina by specifying a Latitude
and Longitude. The Latitude and Longitude of a project site may be obtained from the plans or
by using an Interactive Internet search tool. Typical Latitude and Longitude for South Carolina
cities are provided in Table 11-7 for reference.
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Table 11-7, Latitude and Longitude for South Carolina Cities
SC City
Anderson, SC
Beaufort, SC
Charleston, SC
Columbia, SC
Florence, SC
Georgetown, SC
Greenville, SC
Latitude
34.50
32.48
32.90
33.95
34.18
33.83
34.90
Longitude
82.72
80.72
80.03
81.12
79.72
79.28
82.22
SC City
Greenwood, SC
Myrtle Beach, SC
Nth Myrtle B, SC
Orangeburg, SC
Rock Hill, SC
Spartanburg, SC
Sumter, SC
Latitude
34.17
33.68
33.82
33.50
34.98
34.92
33.97
Longitude
82.12
78.93
78.72
80.87
80.97
81.96
80.47
The site-specific hazard PGA and PSA are generated by the GDS for every project using
Scenario_PC (2006) (Chapman, 2006). Scenario_PC generates seismic hazard data in a
similar format as that generated by the USGS. The designer must obtain a SC Seismic Hazard
request form and submit it to the GDS. A copy of the form is included in Appendix A. The SC
Seismic Hazard request form requires that the designer provide the following information.




SCDOT Project Name and Project Number
Latitude and Longitude of Project Site
Probability of Exceedance for Earthquake Design Event being analyzed
Site Condition: Geologically Realistic or Hard-Rock Basement Outcrop
The geotechnical engineer is required to provide documentation for the selection of the Site
Condition (Geologically Realistic or Hard-Rock Basement Outcrop) used.
A sample of the Seismic Hazard information generated by Scenario_PC (2006) for Columbia,
SC is shown in Figure 11-13.
THE NAME OF THE DIRECTORY CONTAINING THIS FILE
AND ALL ASSOCIATED OUTPUT FILES IS: Columbia
3% PROBABILITY OF EXCEEDANCE (For 75 year Exposure)
FOR GEOLOGICALLY REALISTIC SITE CONDITION
RESULTS OF INTERPOLATION
Site Location: 33.9500 N 81.1200 W
Nearest Grid Point: 34.0000 N 81.1250 W Distance From Site:
Thickness of sediments, meters: 262.162
0.5Hz
6.36404
1.0Hz
18.97654
PSA and PGA as Percentage of g
2.0Hz
3.3Hz
5Hz
6.7Hz
30.64109 40.70470 46.59745 45.10500
5.56 Km
13Hz
40.47712
PGA
19.61478
Figure 11-13, Scenario_PC (2006) Sample Output for Columbia, SC
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In order to provide the designer with an overview of the South Carolina’s probabilistic seismic
hazard, probabilistic seismic hazard contour maps for the FEE and SEE design events for PGA,
PSA for the short-period, Ss, (5 Hz = 0.2 seconds), and PSA for the long-period, S1, (1 Hz = 1.0
second) have been included in this Chapter. The PGA and PSA values as a percentage of
gravity (g) have been placed in contours and overlaid over a South Carolina map. FEE seismic
hazard contour maps are provided for PGA, Ss, and S1 in Figures 11-14, 11-15, and 11-16,
respectively. SEE seismic hazard contour maps are provided for PGA, Ss, and S1 in Figures
11-17 11-18, and 11-19, respectively. FEE and SEE peak ground accelerations (PGA) and
pseudo-spectral accelerations (PSA) (generated by Scenario_PC 2006) for selected cities in
South Carolina have been plotted at either the B-C boundary (geologically realistic) or hard rock
basement outcrop in Figures 11-20 and 11-21. The seismic hazard contour maps and the
sampling of the PSA curves for various cities are provided for information only and must not be
used for design of any structures in South Carolina.
August 2008
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Geologically Realistic Site Condition
Hard-Rock Basement Outcrop Site Condition
Figure 11-14, PGA (%g) - 15% PE in 75 Years (10% PE-50 Yr)
(Chapman and Talwani, 2002)
11-20
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Geologically Realistic Site Condition
Hard-Rock Basement Outcrop Site Condition
Figure 11-15, Ss Spectral Acceleration (%g) - 15% PE in 75 Years (10% PE-50 Yr)
(Chapman and Talwani, 2002)
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Geologically Realistic Site Condition
Hard-Rock Basement Outcrop Site Condition
Figure 11-16, S1 Spectral Acceleration (%g) - 15% PE in 75 Years (10% PE-50 Yr)
(Chapman and Talwani, 2002)
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Geologically Realistic Site Condition
Hard-Rock Basement Outcrop Site Condition
Figure 11-17, PGA (%g) - 3% PE in 75 Years (2% PE-50 Yr)
(Chapman and Talwani, 2002)
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Geologically Realistic Site Condition
Hard-Rock Basement Outcrop Site Condition
Figure 11-18, Ss Spectral Acceleration (%g) - 3% PE in 75 Years (2% PE-50 Yr)
(Chapman and Talwani, 2002)
11-24
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Geologically Realistic Site Condition
Hard-Rock Basement Outcrop Site Condition
Figure 11-19, S1 Spectral Acceleration (%g) - 3% PE in 75 Years (2% PE-50 Yr)
(Chapman and Talwani, 2002)
August 2008
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Figure 11-20, FEE PSA Curves for Selected South Carolina Cities
Figure 11-21, SEE PSA Curves for Selected South Carolina Cities
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11.9.3
SC GEOLOGY AND SEISMICITY
Earthquake Deaggregation Charts
The ground motion hazard from a probabilistic seismic hazard analysis can be deaggregated to
determine the predominant earthquake moment magnitude (MW) and distance (R) contributions
from a hazard to guide in the selection of earthquake magnitude, site-to-source distance, and in
development of appropriate time histories. The deagregation charts can be obtained by either
of the following methods:


SCDOT Scenario_PC (2006)
USGS Interactive Earthquake Deaggregation 2002
The SCDOT Scenario_PC (2006) generates the interpolated results from the USGS
Deaggregation 2002 data. A sample deaggregation output is provided in Figure 11-22 that was
generated along with the SC Seismic Hazard results shown in Figure 11-13.
Interpolated results from USGS Deaggregation 2002
Freq. R(mean) km
mag(mean)
eps0(mean) R(modal) km
PGA
58.6
6.31
.44
125.4
5 Hz
77.3
6.64
.68
125.1
1 Hz
113.1
7.06
.74
125.0
mag(modal)
7.31
7.30
7.30
eps0(modal)
1.23
1.05
.81
Figure 11-22, Scenario_PC (2006) Deaggregation – Columbia, SC
Deaggregation of the seismic hazard can also be obtained from the USGS 2002 Interactive
Deaggregation web site. The steps required to obtain USGS web site deaggregations are listed
in Table 11-8. The project site Latitude and Longitude are obtained in the same manner as
described in Section 11.9.2.
Table 11-8, USGS Interactive Deaggregation of Seismic Hazard
Step
1
2
3
Action
Access the USGS 2002 Interactive Deaggregations website to obtain the hazard deaggregation
response for PGA and PSA frequencies.
Website: http://eqint.cr.usgs.gov/deaggint/2002/index.php
Complete the screen form (See Figure 11-23):
Enter “Site Name”
Enter “Site Latitude and Longitude (negative) Coordinates”
Select “Return period based on design earthquake”:
10% PE 50 yrs = 15% PE 75 yrs (FEE)
2% PE 50 yrs = 3% PE 75 yrs (SEE)
Select “SA Frequency”:
5.0 Hz = 0.2 sec for Short-Period SA (SS)
1.0 Hz = 1.0 sec for Long-Period SA (S1)
PGA
Select Geographic Deaggregation – Optional (Fine Angle, Fine Distance)
Select Stochastic Seismograms – Select None
Select Generate Output
Documents Generated:
Report - Hazard Matrix Data File (Figure 11-24)
Deaggregation - Deaggregation Seismic Hazard Graph (Figure 11-25)
Geographic Deaggregation – Optional (Figure 11-26)
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Figure 11-23, Interactive Deaggregation Input Screen
(USGS 2002 Earthquake Deaggregations)
The Deaggregated Seismic Hazard Graph for the data entered in Figure 11-23 is shown in
Figure 11-24. An abridged sample of the Hazard Matrix Data File is shown in Figure 11-25.
The geographic deaggregation is shown in Figure 11-26.
Figure 11-24, Columbia, SC Deaggregation SEE (3% PE in 75 Years, 1Hz PSA)
(USGS 2002 Earthquake Deaggregations)
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********************Central or Eastern U.S. Site ********************************
PSHA Deaggregation. %contributions. ROCK site: Columbia, _SC long: 81.120 d W.,
lat: 33.950 N.
USGS 2002-2003 update files and programs. Analysis on DaMoYr:31/10/2006
Return period: 2475 yrs. 0.20 s. PSA =0.5510
g.
#Pr[at least one eq with median motion>=PSA in 50 yrs]=0.00397
DIST(km) MAG(Mw) ALL_EPS EPSILON>2 1<EPS<2 0<EPS<1 -1<EPS<0 -2<EPS<-1 EPS<-2
181.3
7.18
0.080
0.042
0.039
0.000
0.000
0.000
0.000
209.8
7.15
0.056
0.043
0.013
0.000
0.000
0.000
0.000
12.8
7.39
0.915
0.001
0.061
0.354
0.361
0.131
0.007
34.7
7.39
1.495
0.033
0.283
0.712
0.443
0.023
0.000
60.8
7.39
0.753
0.042
0.268
0.434
0.009
0.000
0.000
89.2
7.32
2.696
0.287
1.621
0.788
0.000
0.000
0.000
122.2
7.30
15.286
2.376
11.030
1.879
0.000
0.000
0.000
130.9
7.30
4.347
0.958
3.389
0.000
0.000
0.000
0.000
. . .
Additional output data omitted
. . .
Summary statistics for above 0.2s PSA deaggregation, R=distance, e=epsilon:
Mean src-site R=
76.8 km; M= 6.64; eps0=
0.67. Mean calculated for all
sources.
Modal src-site R= 122.2 km; M= 7.30; eps0=
0.99 from peak (R,M) bin
Gridded source distance metrics: Rseis Rrup and Rjb
MODE R*= 122.2km; M*= 7.30; EPS.INTERVAL: 1 to 2 sigma % CONTRIB.= 11.030
Principal sources (faults, subduction, random seismicity having >10% contribution)
Source Category:
% contr.
R(km)
M
epsilon0 (mean
values)
Charleston Broad Zone
19.64
126.9
7.29
1.09
Charleston Narrow Zone
24.38
125.0
7.29
1.06
CEUS gridded seism.
55.98
38.2
6.12
0.36
Individual fault hazard details if contrib.>1%:
********************Central or Eastern U.S. Site ********************************
Figure 11-25, Abridged Seismic Hazard Matrix Data – Columbia, SC
(USGS 2002 Earthquake Deaggregations)
Figure 11-26, Geographic Deaggregation (Optional)
(USGS 2002 Earthquake Deaggregations)
August 2008
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The earthquake deaggregations typically provide the source category, percent contribution of
the source to the hazard, site-to-source distance (R), mean and modal moment magnitude (M),
and epsilon (). Mean moment magnitudes (MW) that cover several sources are typically not
used since it is an overall average of earthquakes and does not appropriately reflect magnitude
of the hazard contribution within a specific seismic source. Mean moment magnitude (MW)
values listed with respect to principal sources can be used. The epsilon () parameter is as
important to understanding a ground motion as is the moment magnitude (MW) and the distance
(R) values for the various sources. The epsilon () parameter is a measure of how close the
ground motion is to the mean value in terms of standard deviation ().
The epsilon o
parameter is provided for ground motions having a fixed probability of exceedance (PE). If a
structure is designed for an earthquake with magnitude MW that occurs a distance R from your
site and the o = 0.0, then the structure was designed to resist a median motion from this source.
If the o = 1.0, then the structure was designed to resist a motion one standard deviation (+1)
greater than the median motion. Consequently, if the o = -1.0, then the structure was designed
to resist a motion one standard deviation (-1) less than the median motion. Predominance of
a modal earthquake source is generally indicated if the epsilon () is within 1 standard
deviation (1).
For additional information on the interpretation of the deaggregation data, the designer should
refer to the information provided at the USGS 2002 Interactive Deaggregation web site. The
method chosen to deaggregate the South Carolina seismic hazard should be based on the
intended use of the deagregation data. For example, the Scenario_PC (2006) deaggregations
are sufficient to select the earthquake moment magnitude (MW) and site-to-source distance (R)
for liquefaction potential analyses and lateral spreading analyses. When performing a
site-specific response analysis, the 2002 USGS Interactive Deaggregations are more detailed
and informative and should therefore be used to obtain the earthquake moment magnitude (MW)
and site-to-source distance (R) used to generate the ground motion time histories. Further
guidance in the method of obtaining and interpreting the earthquake deagregation data is
provided in Chapter 12 and in Section 11.9.4, Ground Motions.
11.9.4
Ground Motions
Ground motions are required when a site-specific design response analysis and/or a
site-specific seismic deformation analysis is being performed. These ground motions are
developed from a site-specific ground shaking characterization that generates a time history.
Time histories can be either recorded with seismographs or synthetically developed. Since the
Charleston 1886 earthquake occurred, an earthquake with a magnitude of +7 has not occurred
in South Carolina and therefore no seismograph records are available for strong motion
earthquakes in South Carolina. SCDOT has chosen to generate synthetic project-specific time
histories based on the SC Seismic Hazard study recently completed for SCDOT. The ground
motion predictions used in the study are based on the results of recent work involving both
empirical and theoretical modeling of Eastern North American strong ground motion. Even
though the strong motion database for the East is small compared to the West, the available
data indicate that high frequency ground motions attenuate more slowly in the East than in the
West.
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Synthetic ground motions can be developed using an attenuation model. The ground motions
on hard rock produced from the SCDOT Seismic Hazard program Scenario_PC (2006) uses a
stochastic model that uses weighted (w) attenuation relationships from 1987 Toro et al.
(w=0.143), 1996 Frankel et al. (w=0.143), 1995 Atkinson and Boore (w=0.143), 2001 Somerville
et al. (w=0.286), and 2002 Campbell (w=0.286) for the characteristic earthquake events with
magnitudes ranging from 7.0 to 7.5. For the non-characteristic earthquake events with
magnitudes less than 7.0, the following weighted prediction equations were used, 1977 Toro et
al. (w=0.286), 1996 Frankel et al. (w=0.286), 1995 Atkinson and Boore (w=0.286), and 2002
Campbell (w=0.143).
The location of the ground motion is dependent on the Site Condition (Geologically Realistic or
Hard-Rock Basement Outcrop) selected in Section 11.9.2. Table 11-9 provides the location
where the ground motions are computed based on the Site Condition selected and Geologic
Unit.
Table 11-9, Location of Ground Motion
Site
Condition
Geologically
Realistic
Hard-Rock
Basement
Outcrop
(1)
Geologic Unit (1)
Location of Ground Motion
Piedmont /
Blue Ridge
(Zone I)
Generated at a hypothetical outcrop of weathered rock
(Vs = 8,200 ft/sec) equivalent to
Site Class A (Vs > 5,000 ft/sec)
Coastal Plain
(Zone II)
Generated at a hypothetical outcrop of firm Coastal Plain
sediment (Vs = 2,500 ft/sec) equivalent to the B – C Boundary
Piedmont /
Blue Ridge
(Zone I)
Coastal Plain
(Zone II)
Generated at a hard-rock basement outcrop
(Vs = 11,500 ft/sec) equivalent to
Site Class A (Vs > 5,000 ft/sec)
For geologic unit locations see Figure 11-1 and 11-3 and for Site Condition locations see Figure 11-12.
The time histories are generated based on project specific information using Scenario_PC
(2006). The consultant must submit a SC Ground Motion request form to the GDS to obtain
project specific time histories. The SC Ground Motion request form requires that the designer
provide the following information.







SCDOT Project Name and Project Number
Latitude and Longitude of Project Site
Probability of Exceedance for Earthquake Design Event being analyzed
Site Condition: Geologically Realistic or Hard-Rock Basement Outcrop
Sediment Thickness: If other than default thickness generated from Scenario_PC
Scaling Method: Scaling of the time series to match Uniform Hazard, PGA, or PSA
Moment magnitude (Mw) and epicenter site-to-source distance (R)
The sediment thickness may be changed from the default value if a site-specific geotechnical
investigation indicates that the sediment thickness is different from the value generated in the
Scenario_PC (2006) output.
August 2008
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The method of scaling the time series to match a Uniform Hazard Spectrum (UHS), PGA, or a
PSA frequency is primarily dependent on the results of the earthquake deaggregation described
in Section 11.9.3. When the uniform hazard is dominated by a well-defined modal earthquake
event, the method of scaling the time series should be to match the UHS.
The Coastal Plain will typically be dominated by the 1886 Charleston earthquake seismic source
as can be seen in Figure 11-27, Florence, SC Deaggregation FEE (USGS 2002). The
earthquake deagregation chart in Figure 11-27 indicates that the FEE 1Hz PSA design
earthquake would have a modal source site with a Moment Magnitude (Mw) of 7.30 with an
epicenter site-to-source distance (R) of 87.1 km and an epsilon (o) parameter of –0.85. The
SEE 1Hz PSA design earthquake for Florence, SC in Figure 11-28 indicates a modal source
site with a Moment Magnitude (Mw) of 7.30 with an epicenter site-to-source distance (R) of 36.2
km and an epsilon (o) parameter of 0.01. As a result of the predominance of the 1886
Charleston Earthquake seismic source in the Coastal Plain geological unit, the time series
generated for most project sites in the Coastal Plain should be scaled to match the UHS. By
contrast, the FEE and SEE Anderson, SC Deaggregation (USGS 2002), shown in Figures 11-29
and 11-30, respectively, show several earthquakes that may be of significance to evaluating
seismic hazards at the project site. Table 11-10 provides a summary of FEE 1Hz potential
seismic sources that may be used for scaling the time series. All FEE 1Hz seismic sources
appear to be equally predominant epsilons () within 1 standard deviation (1).
Table 11-10, FEE 1Hz PSA Deaggregation Summary - Anderson, SC
%
R
Seismic Source Site
MW
Contribution
Distance, km
1886 Charleston Seismic Source
28.7
235
7.26
New Madrid (NMSZ)
12.5
640
7.72
CEUS
58.8
184
6.52
Total Contribution % =
100.0
----Modal Source Site
--282
7.30
o
0.19
0.82
0.34
--0.09
Table 11-11 provides a summary of SEE 1Hz potential seismic sources that may be used for
scaling the time series. The SEE 1Hz CEUS seismic source site appears to be predominate
with an epsilons () of 0.65.
Table 11-11, SEE 1Hz PSA Deaggregation Summary - Anderson, SC
%
R
Seismic Source Site
MW
Contribution
Distance, km
1886 Charleston Seismic Source
23.70
238
7.30
New Madrid (NMSZ)
6.9
644
7.77
CEUS
64.4
125
6.72
Total Contribution % =
100.0
----Modal Source Site
--282
7.30
o
1.21
1.77
0.65
--1.17
Similar deaggregation data can be obtained for PGA or other PSA frequencies. Based on the
type of structure being designed or seismic hazard being analyzed, there may be a need to
develop more than one earthquake seismic source time series and have it matched to the PGA
or a PSA frequency.
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Figure 11-27, Florence, SC Deaggregation FEE (15% PE in 75 Years, 1Hz PSA)
(USGS 2002 Earthquake Deaggregations)
Figure 11-28, Florence, SC Deaggregation SEE (3% PE in 75 Years, 1Hz PSA)
(USGS 2002 Earthquake Deaggregations)
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Figure 11-29, Anderson, SC Deaggregation FEE (15% PE in 75 Years, 1Hz PSA)
(USGS 2002 Earthquake Deaggregations)
Figure 11-30, Anderson, SC Deaggregation SEE (3% PE in 75 Years, 1Hz PSA)
(USGS 2002 Earthquake Deaggregations)
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11.10 REFERENCES
The geotechnical information contained in this Manual must be used in conjunction with the
SCDOT Seismic Design Specifications for Highway Bridges, SCDOT Bridge Design Manual,
and AASHTO LRFD Bridge Design Specifications. The Geotechnical Design Manual will take
precedence over all references with respect to geotechnical engineering design.
AASHTO LRFD Bridge Design Specifications, U.S. Customary Units, 4th Edition, (2007),
American Association of State Highway and Transportation Officials.
Atkinson, G.A. and D.M. Boore, (1995), “Ground motion relations for Eastern North America”,
Bulletin of the Seismological Society of America, v. 85, pp. 17-30.
Boore D.M. and W.B. Joyner, (1991), “Ground motion at deep soil sites in eastern North
America”, Bulletin of the Seismological Society of America, v. 81, pp. 2167-2187.
Campbell, K. W., (2002). “Prediction of strong ground motion using the hybrid empirical method:
example application to eastern North America”, submitted to Bull. Seism.
Soc. Am.
Chapman and Talwani (2002). “Seismic Hazard Mapping for Bridge and Highway Design”,
SCDOT, Referred to in this manual as SCDOT Seismic Hazard Study.
Chapman (2006). “User’s Guide to SCENARIO_PC and SCDOTSHAKE”, SCDOT.
Frankel, A., C. Mueller, T. Barnhard, D. Perkins, E.V. Leyendecker, N. Dickman, S. Hanson and
M. Hopper, (1996), “National seismic-hazard maps; documentation”, United States Geological
Survey Open-File Report 96-532, 110p.
Marple, R.T., and P. Talwani, (1993), “Evidence of possible tectonic upwarping along the South
Carolina Coastal Plain from an examination of river morphology and elevation data”, Geology, v.
21, pp. 651-654.
Marple, R.T., and P. Talwani, (2000), “Evidence for a buried fault system in the Coastal Plain of
the Carolinas and Virginia; Implications for neotectonics in the southeastern United States”,
Geological Society of America Bulletin, v. 112, no. 2, pp. 200-220.
Odum, J.K., Williams, R.A., Stepheson, W.J., and Worley, D.M., (2003). “Near-surface S-wave
and P-wave seismic velocities of primary geological formations on the Piedmont and Atlantic
Coastal Plain of South Carolina, USA”, United States Geological Survey Open-File Report
03-043, 14p.
Snipes, D.S.,W.C. Fallaw, Van Price Jr. and R.J. Cumbest, (1993). “The Pen Branch Fault:
Documentation of Late Cretaceous-Tertiary Faulting in the Coastal Plain of South Carolina”,
Southeastern Geology, 33, No.4, 195-218
South Carolina Department of Natural Resources, Geologic Survey, (2005). “Generalized
Geologic Map of South Carolina 2005,” http://www.dnr.state.sc.us/geology/geology.htm
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South Carolina Department of Natural Resources, Geologic Survey. “Geologic Time Scale for
South Carolina”, http://www.dnr.state.sc.us/geology/images/Time%20scale_pagesize.pdf
South Carolina Department of Natural Resources, Geologic Survey. “Earthquake Intensities By
County”, http://www.dnr.state.sc.us/geology/earthquake_intens.htm
SCDOT Bridge Design Manual (2006), South Carolina Department of Transportation,
http://www.scdot.org/doing/bridge/06design_manual.shtml
SCDOT Seismic Design Specifications for Highway Bridges (2008), South Carolina Department
of Transportation, http://www.scdot.org/doing/bridge/bridgeseismic.shtml
Somerville, P., N. Collins, N. Abrahamson, R. Graves and C. Saikia, (2001), “Ground motion
attenuation relations for the central and eastern United States”, final report to the U. S.
Geological Survey.
Toro, G., and R.K. Mcguire, (1987), “An investigation into earthquake ground motion
characteristics in eastern North America”, Bulletin of the Seismological Society of America, v.
77, pp. 468-489.
United States Geological Service (USGS), “Damaging Earthquakes In the US (1750 – 1996)”,
http://earthquake.usgs.gov/regional/states/us_damage_eq.php
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